Rolls-Royce on Wednesday unveiled designs for its next generation of fuel-efficient plane engines, aimed at powering civilian aircraft of the future.

Two weeks after announcing a shock profit warning with government cutbacks on defence spending impacting its military engines business, the British group revealed plans to build on its successful Trent XWB engine, which is exclusively powering Airbus A350 long-haul passenger planes.

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"A big bulk of the (aircraft cost) efficiency is coming from the engines, so we have an important role to play to support our customers," Eric Schulz, in charge of Rolls' large civilian jet engines unit, said Wednesday in a conference call with reporters attending a media presentation in Derby, central England.

Rolls Royce UltraFan engine design.

Rolls said that Advance, the development name for one of its future engines, will burn at least 20 percent less fuel -- with a corresponding drop in CO2 emissions -- compared with the first generation of Trent engines that entered service in 1995. The Advance could be ready by the end of the decade, it added.

An even more fuel-efficient model, UltraFan, could be ready for service from 2025.

"One simply cannot rush new technology along so it is something that has to be held in store," said aerospace analyst Sandy Morris at financial group Jefferies.

The CTi fan system.

"If there is a snag, it is that we may have to wait up to a decade before we can start to picture the new aircraft onto which the latest-technology engines could be fitted.

Rolls is the sole engine provider for the Airbus A350 XWB, a long-range, wide-body plane that is slated to come into service at the end of the year. It makes engines also for the Airbus A380 super jumbo and Boeing's 787 Dreamliner, competing for business here with US conglomerate General Electric.

Like the Trent XWB, the future engines will make extensive use of light carbon-based composite materials that significantly reduce fuel consumption and costs for manufacturers and airlines.

"They are designed to deliver... even better fuel efficiency, reliability and environmental performance," said Colin Smith, Rolls-Royce director of engineering and technology.

In Derby, where Rolls assembles jet engines for both European planemaker Airbus and its US rival Boeing, the company added that both new engine designs were the result of research and development investment totalling about £1.0 billion ($1.7 billion, 1.2 billion euros) a year across its aerospace and non-aerospace businesses.

In the short term, Rolls faces harder times despite its success in the market for large civilian plane engines.

Earlier this month, the company said that its profit and revenue would flatten in 2014, as government cutbacks on defence spending end the company's decade of rampant growth.

News of a 41-percent slump in annual profits sent Rolls-Royce shares diving earlier in February.

On Wednesday, Schulz shrugged off the impact of a bribery probe over Rolls' operations in Asia.

"I think our customers are confident that the management of this company has the right level of ethics and the right level of processes and governance in place," he told journalists.

Rolls in December revealed that it was facing a formal investigation by Britain's Serious Fraud Office into alleged bribery linked to its overseas operations.

The firm warned that it might be prosecuted over alleged "malpractice" in Indonesia and China after passing on information related to bribery concerns to the office.